There are many scientific and industrial processes which require delivery of a fluid to a surface for treatment of that surface or for removal of soluble materials from that surface. In some of these applications the fluid needs to be delivered in a pulsed manner, with high pressure and low pressure streams of fluid being alternated. In some of these applications the fluid has to be kept in a supercritical phase while the surface is being contacted with the fluid.
One particularly suitable use of the invention apparatus is described in an application for a patent filed on even date herewith covering the invention of certain fluids to be used for removal of photoresist materials from substrates used in the manufacture of integrated circuits or other electronic components.
During manufacture of integrated circuits, commonly referred to as semiconductor chips or microchips, several iterations of a photolithographic process are used. In this manufacturing process, electrically conductive ion implant gates of an electrically conductive barrier layer such as silicon dioxide, silicon nitride or metal is first deposited upon a substrate such as a silicon or gallium arsenide wafer by any of several suitable processes such as thermal oxidation, chemical vapor deposition, sputtering, ion implantation or vacuum evaporation.
After formation or deposition of the electrically conductive barrier layer, a photoresist material is applied to the wafer by any suitable means including, but not limited to, spinning of the wafer to distribute liquid photoresist evenly on the surface of the wafer.
Usually the photoresist material coated wafer is then heated in a "soft bake" or prebake step to improve adhesion of the photoresist material to the substrate surface and/or the barrier layer and to remove solvent from the generally polymeric photoresist material.
After the photoresist is soft baked onto the barrier layer, portions of the soft baked photoresist coated wafer are selectively exposed to high energy light such as high intensity ultraviolet light in a desired pattern defined by a photomask. Developing agents are then used to develop the portions of the photoresist material which were exposed to the high energy light.
When positive photoresist materials are used, the developed portions of the photoresist materials are solubilized by the exposure to the light and development and then are washed away, leaving portions of the barrier layer coated wafer exposed and other portions of the wafer coated with barrier layer underneath the remaining, unexposed and undeveloped photoresist layer.
Conversely, when negative photoresist materials are used, the undeveloped portions of the photoresist materials are selectively removed for exposing selected portions of the barrier material coated substrates in the desired patterns.
Once the pattern of photoresist has been established on the wafer, the wafer is "hard baked" to densify and toughen the photoresist material and improve adhesion to the barrier layer. The exposed substrate and/or barrier material is then etched (removed) by any of several suitable methods, depending upon which materials were used as the barrier layer. Wet chemical etching, dry etching, plasma etching, sputter etching or reactive-ion etching processes may be used. The etching processes remove barrier material which is unprotected by photoresist, leaving both portions of bare wafer and portions of wafer having layered coatings of barrier layer and the photoresist material which protected the barrier layer underneath from the etching process on the surface of the wafer.
The wafer having on its surface the pattern of barrier layer material coated with photoresist material is then treated in an aggressive step to remove the hard baked photoresist material from the remaining pattern of barrier layer material. This has traditionally been done using solvent washes such as halogenated hydrocarbons, mixtures of sulfuric acid and hydrogen peroxide, or highly alkaline mixtures of hydroxides with activators. Use of any of these solvent mixtures produces large undesirable liquid waste streams.
After removal of the hard baked photoresist material, in a final step the substrate with the patterned surface layer on it is washed with deionized water to ensure that all traces of photoresist removal solvents are removed from the wafer surface. This photolithographic process is repeated as many times as needed to produce as many layers of different patterns of the electrically conductive barrier layer material upon the substrate as desired, often creating large waste streams of contaminated water.
There is a need for methods of effectively removing photoresist materials in ways that reduce the amount of undesirable waste streams.
More generally, there is a need for an apparatus and method for providing pulsed fluids to reaction sites or surfaces to be treated with those fluids and, more particularly, there is a need for an apparatus and method for providing pulsed supercritical fluids to surfaces to be treated with the supercritical fluids.
Therefore it is an object of this invention to provide an apparatus and method for providing a pulsed fluid to a reaction site or surface to be treated with the fluid.
It is another object of this invention to provide a method and apparatus for removing photoresist materials used in the manufacture of integrated circuits or other electronic components such as circuit boards, optical waveguides and flat panel displays.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. The claims appended hereto are intended to cover all changes and modifications within the spirit and scope thereof.